Presently, OLED (organic light-emitting diode) is still produced mainly by thermal evaporation. Either manufacturer or user of the evaporation source aims at improving the performance of the evaporation source such as the improvement of the material usage, the reduction of the material cost, and the improved performance of OLED assembly, such as the uniformity of the thickness of the deposited film.
The evaporation source used in the conventional evaporation process includes a point-type evaporation source, a cluster-type linear evaporation source, a single point-type liner evaporation source and a planar evaporation source. The point-type evaporation source generally comprises a crucible for containing evaporating material, above which a substrate is located. When deposited by the point-type evaporation source, the film often presents the following disadvantages: low material utilization, generally lower than 10%; low film uniformity, generally lower than 10%, wherein the uniformity of the film is calculated by the formula: (maximum thickness−minimum thickness)/(maximum thickness+minimum thickness).
In general, the cluster-type linear evaporation source comprises at least two parallelly-arranged crucibles in the shape of an elongated recess, where the different evaporating materials are laid on the bottoms of the two crucibles, respectively. The film formed by virtue of the cluster-type linear evaporation source has good film uniformity (lower than 5%) but poor material utilization (10%-20%).
The planar evaporation source usually comprises a body which has an area equal to or larger than that of the target to be deposited. The film formed by virtue of the planar evaporation source has good material utilization (higher than 40%) but unstable film uniformity (lower than 10%).
As shown in FIG. 1, the conventional single point-type liner evaporation source includes an elongated body 10 where a chamber is structured therein and a plurality of nozzles 12 is formed thereon; and a crucible 20 which is in communication with the center of the bottom of the body 10. When a film is to be deposited on a substrate 30, the crucible 20 is heated by a heating device (not shown), the evaporating material in the crucible 20 is vaporized vapor into the chamber of the body 10, and then is ejected to the substrate 30 through the nozzles 12, finally a film of the evaporating material is formed on the bottom surface of the substrate 30.
In the conventional single point-type liner evaporation source, the crucible 20 is connected to the center of the bottom of the elongated body 10, the concentration of the vaporized vapor materials in the chamber adjacent to the center of the crucible 20 is accordingly higher, while the concentration of the vaporized materials vapor far away from the center of the crucible 20 is lower. That is, the saturated pressure in the chamber is unbalanced, which causes the thickness of the film formed on the substrate 30, particularly at two ends of the substrate 30, is not uniform. Moreover, the film uniformity of a large-size film which is formed by the conventional single point-type liner evaporation source may be even worse.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.